1. Technical Field
Embodiments of the present invention relate to processing of digital images, and more particularly to reducing building lean in stitched images.
2. Background Art
Image mosaics are created by merging multiple digital images. For example, a view of urban Chicago presented to a user by the Google Earth application (available from Google Inc. of Mountain View, Calif.) may be composed of many overlapping individual images, each of a different area of urban Chicago. The overlapping individual images of the different areas are merged together to form a comprehensive view of the entire area. The process of merging two or more individual images is referred to as “stitching.” An image mosaic is referred to as a “stitched image.”
Depending on the view to be illustrated in the stitched image, the type of individual image that is used may be different. One type of image is the “oblique image.” Oblique images are photographic images captured from an aerial platform, such as a low altitude aircraft, at an angle. For example, an aircraft flying over urban Chicago may capture a series of photographs of the area below at an angle. This series of photographs can form a set of oblique images that are later stitched together to form a stitched image of urban Chicago. Due to the angle at which they are captured, oblique images have desirable characteristics such as making the sides of buildings visible while encompassing a large geographic area. In essence, oblique images present three dimensional views of buildings and other structures on the ground that are not visible in straight-down orthographic images. Thus oblique images are particularly useful, for example, in applications where views of the sides of buildings and structures are sought.
However, some types of photographic images of geographic areas, such as oblique images, have characteristics that result in stitched images containing distortions. One such characteristic is that, due to perspective in oblique images, buildings and structures in the left part of the image often appear to lean left while buildings in the right part of the image appear to lean right. In an individual oblique image, this appearance of leaning may not be particularly noticeable. However, when two or more images with building lean are stitched together, the distortions due to building lean can be particularly distracting: For example, in adjacent images in the stitched image, one building can be leaning left while another leans right.
Therefore, methods and systems to reduce the appearance of building lean in stitched images are desired.